Production of aluminum

ABSTRACT

In the production of aluminum by thermally decomposing an alkylaluminum compound with the aid of suitable apparatus, a problem arises with the fouling of such apparatus by the adherence of aluminum particles. Such fouling is reduced by conducting the decomposition within a neutral liquid solvent which is non-reactive with the alkylaluminum compound and is at a high temperature well above the temperature at which the compound normally decomposes in the pure state. In a commercial operation heated surfaces would normally be used to supply heat to the solvent and these surfaces would be highly susceptible to fouling. To further minimize this fouling a continuous process is envisaged where the decomposition occurs in a series of stirred reactors, the solvent in the last reactor being depleted of alkylaluminum compound. This depleted solvent is passed through a heat exchanger and then back to the first reactor. This depleted solvent would not cause fouling of the heat exchanger.

United States Patent [191 Scull, Jr.

[ 1 PRODUCTION OF ALUMINUM 75] lnventor:

21 Appl. No.: 215,804

Related US. Application Data [63] Continuation-impart of Ser. No. 50,878, June 29 1970. abandoned.

152] US. Cl 75/68 C [51] Int. Cl C22b 21/00 [58] Field of Search 75/68 C, (1.5 R, 0.5 A, 75/05 B; 204/193 [56] References Cited UNITED STATES PATENTS 3.165.397 1/1965 Lobo 75/68 C 3.155.493 11/1964 Tanaka 75/68 C 3.102.805 9/1963 Messner 75/68 R 3.578.436 5/1971 Becker 75/68 C 3.552.946 1/1971 Brendel 75/68 C 3.488.148 1/1970 Krinov 204/193 3,165,397 1/1965 Cowles 75/05 A Herbert M. Scull, Jr., Baton Rouge,

[ Jan. 8, 1974 Primary ExaminerL. Dewayne Rutledge Assistant ExaminerPeter D. Rosenberg AtzomeyDonald L. Johnson et al.

[57] ABSTRACT In the production of aluminum by thermally decomposing an alkylaluminum compound with the aid of suitable apparatus, a problem arises with the fouling of such apparatus by the adherence of aluminum particles. Such fouling is reduced by conducting the decomposition within a neutral liquid solvent which is non-reactive with the alkylaluminum compound and is at a high temperature well above the temperature at which the compound normally decomposes in the pure state. In a commercial operation heated surfaces would normally be used to supply heat to the solvent and these surfaces would be highly susceptible to fouling. To further minimize this fouling a continuous process is envisaged where the decomposition occurs in a series of stirred reactors. the solvent in the last reactor being depleted of alkylaluminum compound. This depleted solvent is passed through a heat exchanger and then back-to the first reactor. This depleted solvent would not cause fouling of the heat exchanger.

20 Claims, 1 Drawing Figure PRODUCTION OF ALUMINUM CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U. S. Pat. application Ser. No. 50,878, filed June 29, 1970, and now abandoned.

U. S. Pat. Nos. 3,170,787; 3,155,493 and 2,843,474 teach that high purity aluminum may be produced by thermal decomposition or pyrolysis of an alkylaluminum compound and/or its complex compound. However, it has been found in the practice of the process of these patents that a serious problem develops with the deposition of aluminum particles upon the surface of the reactor and heat exchange apparatus. Such depositions not only prevent the recovery of the aluminum, but also reduce the efficiency of heat transfer. This not only limits the process to being conducted as a batch operation, since it must frequently be shut down to clean out the reactor and heat exchange apparatus, but renders the process generally uneconomical. In accordance with the present invention a process has been developed which is highly economical and which successfully overcomes the above problems. A more complete description of this process follows.

SUMMARY OF THE INVENTION The present invention involves a process for the pro duction of aluminum by thermally decomposing an alkylaluminum compound utilizing suitable apparatus wherein the improvement resides in substantially reducing the quantity of aluminum which adheres to the apparatus by conducting the decomposition within a liquid solvent which is substantially non-reactive with the alkylaluminum compound and is at a temperature substantially above the temperature at which the compound decomposes in the pure state.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic view of the reactor system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides for the production of. aluminum by a process involving the thermal decomposition of alkylaluminum compounds which avoids a'serious problem experienced by the prior art, namely, the adherence of aluminum particles to the exposed walls of the reactor, heat exchanger, and other associated apparatus. This sticking problem makes the recovery of aluminum more difficult and expensive and renders the process uneconomical.

To accomplish the purpose of this invention, a process is provided for manufacturing aluminum which involves heating an alkylaluminum compound having the formula (RR Cl-I-CH AlX, wherein R, and R are either alkyl radicals or hydrogen and X is either hydrogen, R'R CH-CH- radical, and/or a complex compound thereof, up to a temperature at which the compound is decomposed, in a neutral solvent medium. Among the alkylaluminum compounds as above generally identified, di-n-propylaluminum hydride, triisobutylalum inum, diisobutylaluminum hydride, triethylaluminum, diethylaluminum hydride and trimpropylaluminum are preferred. However, the R and R radicals, which may be the same or different, may be other alkyl radicals having up to carbon atoms. For

2 example, tri-n-butylaluminum, di-n-butylaluminum hydride, trihexylaluminum and dihexylaluminum hydride are suitable though less preferred.

The neutral solvent employed in this invention is able to dissolve the alkylaluminum compound, has a boiling point higher than the temperature at which the com pound decomposes in the pure state, and has a suffcient thermal stability at that temperature. Exemplary of the solvent are aliphatic, alicyclic and aromatic hydrocarbons, or mixtures thereof, such as various petroleum fractions boiling above 300 C, paraffin oil, alkylbenzenes, alkylnaphthalenes, diphenyl and the like, all boiling above 300 C. Among these, paraffin oil is preferred.

In accordance with the process of this invention the alkylaluminum compound is heated to a temperature at which it decomposes in the neutral solvent. Preferably. the alkylaluminum compound is added to the solvent which is already heated to a temperature at which the compound is readily decomposed. The temperature is desirably well above the temperature at which the alkylaluminum compound normally decomposes in the pure state. Generally, the decomposition reaction of the invention starts from about 300 C, but the heating temperature may vary preferably within the range of from about 310 C to about 500 C. Such relatively high temperatures reduce sticking of the aluminum particles to expose reaction apparatus. Lower temperatures tend to produce excessive sticking of the aluminum to surfaces, especially heated surfaces.

Fouling of heated surfaces which supply the heat of decomposition is also reduced with or without high temperatures if a portion of the liquid from which all or nearly all of the aluminum alkyl has been removed is withdrawn as a side stream, then heated and returned to the remaining solvent. Removal of the aluminum alkyl is effected by thermally decomposing or reacting the aluminum alkyls in aseries of two or more reactors as shown in the drawing. The alkyl is fed through line 1 to the first reactor 2. A stream from the first reactor is fed to the second reactor 3 through pump 4. A stream from the second reactor which is depleted of aluminum alkyl is passed through the heater 6 by pump 5 and then is returned to the first reactor. This solvent, heated to an elevated temperature, supplies the heat of reaction for the two reactors. A second side stream must be passed either continuously or intermittently through a filter or other solid liquid separating device 8 by pump 7 and then back to the reactors. In this way the building up of large quantities of solid aluminum in the solvent is avoided and the product aluminum is easily removed. The number of reactors required to remove substantially all of the aluminum alkyl from the solvent depends on the rate of decomposition which depends on the particular alkyl and the temperature. Once the aluminum alkyl has been removed from the liquid solvent, the solvent may be heated as high as desired up to its boiling point or even to a vapor. If the solvent is heated to a vapor it is evident that the stream to the heater must then be filtered to remove all aluminum solids. It is alsoevident that advantage is taken of the heat of vaporization of the solvent.

For all embodiments of the invention it is desirable that the neutral solvent be agitated. Thus, the liquid medium may be steadily agitated by an impeller, propeller, turbine or the like. The idea behind this is not only to uniformly disperse the alkylaluminum compound into the solvent once it is added, but also to maintain the solvent in motion at least in areas adjacent to the containing apparatus. Such motion prevents the adherence of particles of aluminum to the walls of the apparatus as they are formed. Regardless of the means employed, the motion imparted to the liquid serves to prevent adherence of the aluminum particles to the reaction apparatus and in combination with other factors of this invention effectively reduces fouling.

Having thus described the invention, the following examples are presented as being descriptive and not limiting of the present invention.

EXAMPLE I 710 Grams of TNPA (trim-propylaluminum) were charged to a l-liter glass autoclave and heated to 240 C by means of an internal electrically heated coil. The TNPA was agitated by two turbine agitators at 1,000 RPM. TNPA was metered into the reactor and the evolved gases were passed through a wet test meter to measure the rate of decomposition. Over a period of 50 minutes, 2.55 gram-moles of TNPA were added and 11.5 gram-moles of gas were evolved. The aluminum was formed primarily as a tenacious paste on the heating coil with a lesser amount sticking to the reaction walls. Very little was dispersed in the liquid.

EXAMPLE ll 270 Grams of paraffin solvent and 100 grams of TNPA were charged to a l-liter glass autoclave and heated to 250 C by means of an internal electrically heated coil. The solvent was agitated by two turbine agitators at 1,000 RPM. TNPA was metered into the reactor and the evolved gases were passed through a wet test meter to measure the rate of decomposition. Over a period of 30 minutes, 0.67 gram-moles of TNPA were added and 3.0 gram-moles of gas were evolved. The aluminum was formed primarily as a tenacious paste on the heating coil with a lesser amount sticking to the reactor walls. The solvent contained very little dispersed aluminum.

EXAMPLE 111 453 Grams of paraffin solvent were added to a 1-liter stainless steel reactor and heated to 320 C by means of an internal electrically heated coil. The solvent was agitated by two turbine agitators at 1,000 rpmJTri-npropylaluminum containing some di-npropylaluminum hydride was metered into the reactor and the evolved gases were passed through a wet gas meter to measure the rate of decomposition. Over a period of 38 minutes 0.82 gram-moles of tri-npropylaluminum were added and 3.3 gram-moles of gas were evolved. The aluminum formed was primarily dispersed in the solvent. Only small quantities adhered to the heating surface and reactor walls and these were easily removed.

EXAMPLE IV 454 Grams of paraffin solvent were added to a l-liter reactor and heated to 390 C as in Example I with similar agitation. The heating coil was turned off and its temperature was allowed to cool to reactor tempera.- ture. Trim-propylaluminum was then added, the heat capacity of the solvent thereby supplying the heat of reaction. Trim-propylaluminum addition was stopped when the temperature of the solvent reached 270 C.

Over a period of 24 minutes 0.58 gram-moles of tri-npropylaluminum was added and the total gas evolved measured 2.15 gram-moles. The results were similar to Example lll.

EXAMPLE V Example 111 is repeated except triisobutylaluminum is substituted for trim-propylaluminum and a decomposition temperature of 350 C is utilized. Good results are achieved.

EXAMPLE Vl Trim-propylaluminum is fed at the rate of 13 pounds per hour to a 5-gallon steel reactor which contains approximately 3.75 gallons of paraffin solvent at a temperature of 310 C. The solvent is agitated by a turbine agitator at 2,500 rpm. A side stream is taken off the reactor at the rate of 2 gallons per minute and passed to a second S-gallon steel reactor which also contains approximately 3.75 gallons of paraffin solvent at a temperature of 310 C which is agitated by a turbine agitator at 2,500 rpm. Decomposition of the trimpropylaluminum is completed in the second reactor. A side stream is taken off the second reactor at the rate of 2 gallons per minute and passed to a heat exchanger where the temperature of the stream is elevated to 320 C. This heated stream is then admitted to the first reactor. A second side stream is taken from the second reactor and filtered to remove 2.25 pounds per hour of aluminum particles. The filtered solvent is returned to the first reactor. Good results are obtained.

What is claimed is:

1. In a process for the production of aluminum by thermally decomposing an alkylaluminum compound utilizing suitable apparatus, the improvement comprising substantially reducing the quantity of aluminum which adheres to said apparatus by conducting the decomposition within a neutral liquid solvent which is substantially non-reactive with said alkylaluminum compound and which has been preheated to a temperature substantially above the temperature at which said compound decomposes in the pure state prior to being introduced into a reaction zone. I

2. The process of claim 1, wherein the decomposition is conducted at a temperature of at least about 270 C.

3. The process of claim 1, wherein the decomposition is conducted at a temperature of from about 310 C to about 390 C.

4. The process of claim 1, wherein the alkylaluminum compound is trim-propylaluminum.

5. The process of claim 1, wherein the solvent is a paraffin oil.

6. The process of claim 1, wherein the solvent is heated by adding heated liquid medium thereto.

7. The process of claim 1, wherein the solvent is heated by withdrawing a part of the solvent, heating suchpart and returning same to be added to the remaining solvent.

8. The process of claim 1, wherein the solvent is heated by withdrawing a part of the solvent, decomposing substantially all alkylaluminum compounds therein, heating such part and returning same to be added to the remaining solvent.

9. The process of claim 1, wherein the alkylaluminum is reacted out before heating reduces fouling on heated surfaces.

10. The process of claim 1, wherein the solvent is maintained in motion at least in areas adjacent said apparatus.

11. The process of claim 1, wherein the solvent is maintained in motion at least in areas adjacent said apparatus by moving same in a stream.

12. The process of claim 1, wherein the alkylaluminum compound is tri-n-propylaluminum, the solvent is paraffin oil which is heated by withdrawing a part of the oil, heating such part and returning same to be added to the remaining oil, and the solvent is agitated at least in areas adjacent said apparatus and seeded with active aluminum particles.

13. A continuous process for the production of aluminum by thermally decomposing an alkylaluminum compound comprising admitting the alkylaluminum compound to a first reaction zone containing a neutral liquid solvent which is substantially non-reactive with said compound and which has been preheated in a heating zone separate from said reaction zone to a temperature sufficient to cause a major portion of said compound to decompose and produce aluminum particles, passing the solvent and the remainingund-ecomposed compound to a second reaction zone wherein a temperature is maintained which is sufficient to cause substantially all of the remaining compound to decompose to produce more aluminum particles, heating said solvent in the heating zone separate from said reaction zone, and readmitting said solvent to said first reaction zone.

14. The process of claim 13, wherein a portion of the solvent containing aluminum particles is continuously removed from-the second reaction zone, filtered to re move the particles and then is heated prior to returning to the first reaction zone.

15. The process of claim 14, wherein the rate of filtration is adjusted by filtering only part of the recycle stream to maintain constant concentrations of aluminum particles in the first and second reaction zones.

16. The process of claim 13, wherein the decomposition is conducted at a temperature of at least about 270 C.

17. The process of claim 13 wherein the decomposi-j tion is conducted at a temperature of from about 310 6 C to about 390 C.

18. A continuous process for producing aluminum by thermally decomposing an alkylaluminum compound, comprising the steps of:

1. heating an inert solvent in a suitable heater to a temperature which is substantially above the decomposition temperature of the alkylaluminum compound to be decomposed, introducing a substantial amount of the inert solvent into a first reactor, and agitating the solvent;

2. adding a quantity of the aluminumalkyl compound to be decomposed into the first reactor and continuing agitation;

3. introducing a substantial amount of the preheated inert solvent into a second reactor, said inert solvent having been heated to a temperature which is substantially above the decomposition temperature of the alkylaluminum compound to be decomposed, and agitating the solvent;

4. transferring the product from the first reactor to the second reactor, and continuing agitation, wherein decomposition of the aluminumalkyl compound is' completed therein;

5. transferring a stream substantially depleted of aluminum alkyl from the second reactor to the heater, where said stream is heated to a temperature which is substantially above the decomposition temperature of the alkylaluminum compound to be decomposed, is readily decomposed and subsequently transferred to the first reactor; and,

6. transferring a second stream from the second reactor to a filter where solid aluminum is removed therefrom and the filtered solvent is returned to the first reactor.

19. The process of claim 18, wherein in addition to the first reactor and second reactor, one or more additional reactors are employed, with the product of the first reactor being transferred to an additional reactor and to each additional reactor in turn and finally to the second or last reactor.

20. The process of claim 18, wherein the inert solvent is heated to a temperature of at least 300 C.

f "UNITED STATES PATENT OFFICE w a CERTIFICATE OF-CORRECTION Patent; No. 3,784,372 Dated January 97 m Herbert M. Scull, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line ll reads "process", should read 1 processes Column l, line 15 reads "surface", should read surfaces Column 2, line 28 reads "expose",

-shou1d read exposed Signed and sealed this 1st day of October 1974-.

( L) Attest:

MCCOY M. GIBSON JR. C. DANN Attesting Officer Commissioner of Patents 

2. The process of claim 1, wherein the decomposition is conducted at a temperature of at least about 270* C.
 2. adding a quantity of the aluminumalkyl compound to be decomposed into the first reactor and continuing agitation;
 3. The process of claim 1, wherein the decomposition is conducted at a temperature of from about 310* C to about 390* C.
 3. introducing a substantial amount of the preheated inert solvent into a second reactor, said inert solvent having been heated to a temperature which is substantially above the decomposition temperature of the alkylaluminum compound to be decomposed, and agitating the solvent;
 4. The process of claim 1, wherein the alkylaluminum compound is tri-n-propylaluminum.
 4. transferring the product from the first reactor to the second reactor, and continuing agitation, wherein decomposition of the aluminumalkyl compound is completed therein;
 5. transferring a stream substantially depleted of aluminum alkyl from the second reactor to the heater, where said stream is heated to a temperature which is substantially above the decomposition temperature of the alkylaluminum compound to be decomposed, is readily decomposed and subsequently transferred to the first reactor; and,
 5. The process of claim 1, wherein the solvent is a paraffin oil.
 6. The process of claim 1, wherein the solvent is heated by adding heated liquid medium thereto.
 6. transferring a second stream from the second reactor to a filter where solid aluminum is removed therefrom and the filtered solvent is returned to the first reactor.
 7. The process of claim 1, wherein the solvent is heated by withdrawing a part of the solvent, heating such part and returning same to be added to the remaining solvent.
 8. The process of claim 1, wherein the solvent is heated by withdrawing a part of the solvent, decomposing substantially all alkylaluminum compounds therein, heating such part and returning same to be added to the remaining solvent.
 9. The process of claim 1, wherein the alkylaluminum is reacted out before heating reduces fouling on heated surfaces.
 10. The process of claim 1, wherein the solvent is maintained in motion at least in areas adjacent said apparatus.
 11. The process of claim 1, wherein the solvent is maintained in motion at least in areas adjacent said apparatus by moving same in a stream.
 12. The process of claim 1, wherein the alkylaluminum compound is tri-n-propylaluminum, the solvent is paraffin oil which is heated by withdrawing a part of the oil, heating such part and returning same to be added to the remaining oil, and the solvent is agitated at least in areas adjacent said apparatus and seeded with active aluminum particles.
 13. A continuous process for the production of aluminum by thermally decomposing an alkylaluminum compound comprising admitting the alkylaluminum compound to a first reaction zone containing a neutral liquid solvent which is substantially non-reactive with said compound and which has been preheated in a heating zone separate from said reaction zone to a temperature sufficient to cause a major portion of said compound to decompose and produce aluminum particles, passing the solvent and the remaining undecomposed compound to a second reaction zone wherein a temperature is maintained which is Sufficient to cause substantially all of the remaining compound to decompose to produce more aluminum particles, heating said solvent in the heating zone separate from said reaction zone, and readmitting said solvent to said first reaction zone.
 14. The process of claim 13, wherein a portion of the solvent containing aluminum particles is continuously removed from the second reaction zone, filtered to remove the particles and then is heated prior to returning to the first reaction zone.
 15. The process of claim 14, wherein the rate of filtration is adjusted by filtering only part of the recycle stream to maintain constant concentrations of aluminum particles in the first and second reaction zones.
 16. The process of claim 13, wherein the decomposition is conducted at a temperature of at least about 270* C.
 17. The process of claim 13, wherein the decomposition is conducted at a temperature of from about 310* C to about 390* C.
 18. A continuous process for producing aluminum by thermally decomposing an alkylaluminum compound, comprising the steps of:
 19. The process of claim 18, wherein in addition to the first reactor and second reactor, one or more additional reactors are employed, with the product of the first reactor being transferred to an additional reactor and to each additional reactor in turn and finally to the second or last reactor.
 20. The process of claim 18, wherein the inert solvent is heated to a temperature of at least 300* C. 